Classes vs Objects

Part of the Object Oriented Programming section of Coddy's GDScript journey. Lesson 3 of 65.

A class and its objects hold different things. A const in a class belongs to the class itself: there is one value, and you read it through the class name without creating an object.

# dog.gd
class_name Dog
extends RefCounted

const SPECIES = "Canis familiaris"
var dog_name: String = "Unnamed"
var breed: String = "Unknown"

print(Dog.SPECIES) # Canis familiaris

The var lines describe what each object holds. Every object created with new() gets its own copy of these variables, starting from their default values:

var dog1 := Dog.new()
var dog2 := Dog.new()
dog1.dog_name = "Nicky"
dog1.breed = "Husky"
print(dog1.dog_name) # Nicky
print(dog2.dog_name) # Unnamed

Changing dog1 leaves dog2 as it was. An object can read the constant too: dog1.SPECIES is the same value as Dog.SPECIES.

An object has only the variables its class declares. dog1.color = "brown" stops the program with an error, because Dog has no color variable. Every variable an object needs goes into the class.

Challenge

Easy

Complete the class Student in student.gd:

a constant SCHOOL with the value "Godot High School", shared by the whole class
a String variable student_name
a String variable grade that starts as "N/A"

The supplied code reads how many students follow, then one line per student: a name, optionally followed by a space and a grade. It creates a Student for each line, sets its name, and sets its grade only when the line has one. Then it prints Student.SCHOOL and every student. For the lines Alice A and Bob it prints:

School: Godot High School
Alice has grade A
Bob has grade N/A

Your code goes in student.gd. main.gd holds the supplied input/output code and cannot be edited.

Try it yourself

extends Node

func _ready():
	# Supplied input/output code: keep it as it is
	var count := int(OS.read_string_from_stdin())
	var students: Array[Student] = []
	for i in count:
		var parts := OS.read_string_from_stdin().split(" ", false)
		var student := Student.new()
		student.student_name = parts[0]
		if parts.size() > 1:
			student.grade = parts[1]
		students.append(student)
	print("School: %s" % Student.SCHOOL)
	for student in students:
		print("%s has grade %s" % [student.student_name, student.grade])